The present invention is related to cutters for cross cutting of reeled webs, and more particularly of paper, aluminium, coupled paper-aluminium and the like webs.
In the field of such web cutters three different systems are presently known. A first system consist of a vertically displacable guillotine knife whose down stroke across the web performs severing thereof. Evidently, descent of the guillotine knife requires stopping the web advancement, whereby this systems involves an excessively long operative time. It has also been proposed to make the cutting assembly movable and to displace it along the advancement direction of the web to avoid stopping thereof upon severing. However this solution is constructively complicated and thus expensive.
A second system employs a rotary knife, constituted by a plate mounted on the generating line of a blade-carrier cylinder, co-operating with a stationary counter blade. At each revolution, the blade projecting from the cylinder encounters the stationary counter blade, grazing it so as to cut the web interposed between the blade and the counter blade. This system is affected by precision problems and above all involves imperfections along the cut edges of the web caused by the fact that the counter blade is stationary and, as a consequence, cutting involves a more or less remarkable web tearing effect.
The third system, also of a rotary type, includes a blade and a counter blade which are both rotary. More particularly, the cutters of this type comprise a web advancement assembly, a rotary cutting assembly including a blade and a counter blade arranged at opposite sides of the web advancement path and rotatable around respective rotation axes placed transversely of said advancement path, and motor driven means to operate rotation of the blade and of the counter blade around said rotation axes in synchronism with the advancement of the web and to place said blade and counter blade in a mutually facing angular position for cutting the web.
This third system, while overcoming the drawbacks linked to the previous systems, does not however enable achieving results in terms of cutting precision and production speed which would instead be desirable.
Moreover in the case of the second and of the third system the blade and possibly the counter blade are as a rule continuously rotated during advancement of the web, which involves evident limits in connection with the maximum length of the web, deriving from the maximum diameter of the blade cylinder carrier (and possibly of the counter blade cylinder carrier) which can be applied to the cutter.
The object of the present invention is to provide a cutter for cross cutting of reeled webs of the above disclosed third type, designed to achieve appreciably improved results both as far as cutting precision, repeatability and uniformity is concerned, and in connection with increased operative speed, and which moreover is not affected by any limits related to the web cutting length.
According to the invention, this object is achieved essentially by virtue of the fact that the rotation axes of the blade and of the counter blade are further displaceable relative to each other perpendicularly to the web, of the fact that actuator means are provided to operate mutual approaching between said rotation axes when said blade and said counter blade are located in correspondence of said angular cutting position, and of the fact that said blade and said counter blade are rotated only at the time of cutting.
Due to this idea of solution, web cutting carried out between the blade and the counter blade is in practice performed by a shearing action, with a precision which is same and even greater than that afforded by the guillotine systems disclosed in the above, but with an operative speed which is at least same and even greater than that of the rotary systems, without any limits to the cutting length.
This result can be achieved not only in connection with cuts perpendicular to the longitudinal edges of the web, but even as far as oblique cuts are concerned, providing a cutting assembly mounting capable to be angularly shifted relative to the web for instance between 0xc2x0 and 45xc2x0.
According to a preferred embodiment of the invention, said actuator means comprise a rotary cam system operating against the action of return resilient means. Moreover in the preferred embodiment of the invention the rotation axis of the blade is movable while the rotation axis of the counter blade is stationary.
The cutter according to the invention can be advantageously employed for cutting reeled webs made of aluminium, paper, coupled paper-aluminium and the like, and can be installed in lines along with printing machines, spreading apparatus, spraying machines, coupling devices etc.